Capacitation includes changes which sperm undergo after leaving the male reproductive tract up tp, but not including, the acrosome reaction. Those changes although poorly understood are essential for fertilization. Considerable evidence indicates the sperm surface is modified during capacitation. We have previously shown that capacitated or trypsinized guinea pig sperm are more agglutinable by certain lectins than uncapacitated sperm. These observations could be explained by activation of a surface proteinase during capacitation. Such a proteinase could remove sperm coating proteins and lead to a reorganization of sperm surface architecture. A similar situation has been reported in transformed cells. We propose to examine molecular aspects of sperm capacitation and to determine if a surface proteinase functions in capacitation. Ferritin conjugated lectins will be used to establish if the number and/or mobility of lectin receptors increases during capacitation; these results will explain why lectin induced agglutinability increases. If a surface proteinase exposes new receptors or alters membrane protein mobility, then proteinase inhibitors should prevent these processes. Experiments using a broad spectrum of non-toxic proteinase inhibitors will be done to establish if this is the case. We will next attempt to demonstrate the presence of a sperm surface proteinase biochemically. Living intact sperm will be tested before and after capacitation (but before the acrosome reaction) for their ability to hydrolyze H3-acetylated hemoglobin. Finally, the exact location of surface proteinase will be determined ultrastructurally with the silver proteinate method. The proposed work will bring us closer to understanding the molecular basis of sperm capacitation and the role of sperm proteinases in fertilization. From such understanding will come better technology for control of these processes and fertility regulation. The lectin agglutination assay, for example, may eventually be useful as a clinical assay for testing sperm fertility.